Production of carbon fibres



March 17, 1970 T. LLOYD ETAL rnonucwlon or CARBON FIBRES Filed June 26.1967 INVENTORS THOMAS LLOYD ATTORNEYS PATRICK MC MULLEN United StatesPatent US. Cl. 8151.2 10 Claims ABSTRACT OF THE DISCLOSURE A device forfeeding fibres of organic polymer material to an oxidizing oven in theprocess of manufacture of carbon fibres from the fibres. The deviceincludes tensioned fibre supply means and a pair of rollers adjacent theoven for supporting successive separated turns of fibres from the supplymeans. At least one of the rollers is driven at a rate such that thefibre is held taut in passing from the rollers to driven means withinthe oven so that the fibre can undergo at most a controlled and limitedchange in length compared with its original length. Brake means areoperable to apply a braking force to the fibres supplied to the rollersto maintain same at a tension suflicient to prevent slippage of thefibres on the rollers.

This invention relates to apparatus for feeding fibres of organicpolymer material to an oxidising oven in a process for the manufactureof carbon fibres from said material. A tow of fibres passes from abraked supply spool in successive turns over a pair of driven rollersoutside the oven. The fibres are drawn into the oven at a predeterminedrate and the rollers are driven at such a rate to feed the fibres to theoven so that the tension in the fibres extending from the rollers intothe oven is accurately controlled.

This invention relates to apparatus for feeding fibres of organicpolymer material to an oxidising oven in a process for the manufactureof carbon fibres from fibre tow of organic polymer material.

In co-pending US. patent application Ser. No. 648,916 processes aredisclosed for the continuous production of high strength carbon fibresfrom fibres of anorganic polymer of a type in which the linear moleculescan be cross-linked, for example by oxidation by heating at below theirmelting point in an oxidising atmosphere, or, if the polymer fibre is ofa type having no melting point, heating in an oxidising atmosphere at atemperature which allows oxidation to proceed in a controlled manner,and which upon subsequent carbonising in a nonoxidising atmosphere yieldcarbon fibres which are highly crystalline with the C axis of thecrystallites preferentially aligned normal to the fibre longitudinalaxis, which include an oxidising step in which a continuous length offibre passing from an external source into an oxidising atmosphere in anoven wherein it is heated to a temperature of 200-250 C. (or notappreciably above 250 C.) travels therein between supporting and drivingmeans which support and drive the fibre so as to maintain the portion ofthe fibre travelling between the supporting and driving means undersufficient tension to reduce or prevent shrinkage of the fibre or toelongate it and whereby each unit length of fibre remains in the ovenfor the required period.

As disclosed in the above referred to US. patent application Ser. No.648,916 the fibre is fed under very accurately controlled tension to thesupporting means within the oxidising oven.

3,500,482 Patented Mar. 17, 1970 ice It has been found in practice to bedesirable that the fibre entering the oven and on its way to but not yetacted on by the supporting and driving means should be prevented fromany undesirable shrinking or stretching due to its temperature on entrybeing raised from the ambient temperature outside the oven towards the200"- 250 C. range within the oven.

The present invention is concerned with the provision of apparatus forfeeding the fibre to be treated to the oven in which oxidation takesplace as referred to above under controlled tension whereby any tendencyto shrinkage or stretch of the fibre may be controlled.

In apparatus for feeding fibres of an organic polymer material of thetype referred to, to an oxidising oven through which they are drawn at apredetermined rate for oxidation as disclosed in co-pending US. patentapplication Ser. No. 648,916, according to the present invention, a pairof equal diameter supporting rollers at least one of which is driven arelocated immediately outside the oven adjacent the inlet to the oventhrough which the fibre passes and the fibre passes over both of theseex ternal supporting rollers from one to the other several times beforepassing to the oven from the external supply.

The fibre is driven by the external rollers at a speed in relation tothe speed of drawing the fibres through the oxidising oven such that thelength of fibre extending from the external rollers to take up meanswithin the oven is maintained under controlled tension.

To avoid damage to the fibres during their passage over the externalsupporting rollers the rollers are supported with their axes of rotationin parallel planes blit skewed with respect to each other,'on the wellknown thread advancing principle, so that succeeding turns of fibre onthe rollers do not contact each other.

A controlled tension is applied to the fibre between an external sourceand the up-strearn supporting roller by tensioning means whichconveniently comprise a variabletorque coupling such as a fluid couplingassociated with the external supply source or a magnetic clutch. Thistension is set so that there is substantially no slippage of fibre inits passage over the external supporting rollers and so that unduetension is not applied to the fibre.

One preferred arrangement of apparatus for feeding fibres according tothe invention is illustrated by the accompanying diagrammatic drawingwhich is a sectional,

side elevation.

Part of the wall of an oxidising oven of the type disclosed inco-pending US. patent application Ser. No. 648,916 is shown at 11 and,within the oven, the first supporting and driving roller 12 of the firstof two pairs of such rollers. An inlet for air to the oven is providedat 13. A pair of rollers 14, 15, of the same diameter as the roller 12,are supported on shafts 16, 17, for rotation in a frame shown generallyat 18 with their rotation axis in parallel planes but skewed as shown.

The shaft 17 carries a bevel gear wheel 19 for engagement with acorresponding bevel wheel (not shown) driven by a common driving shaft23 which also drives the roller 12. A supply spool 20 is supported forrotation on a shaft 21 and is controlled through a variable torquecoupling 22 as will later be described.

In operation a tow of fibre is wound onto the rollers which comprise thesupporting and driving means for the fibres within the oven 11.asdescribed in the above referred to co-pending application, only one suchroller being shown at 12. One end of the fibre tow is then passed outthrough the air inlet 13 and wound five times over the rollers 14, 15from one to the other in elongated loops with succeeding loops separatedfrom each other. The end of the tow is then joined to an end of the towof fibre on the supply spool 20. The oven is now closed and the rollers15, 12 and the corresponding roller (not shown) to the roller 12 'withinthe oven are driven at the same speed. The take up spool down-stream ofthe oven and referred to in the co-pending application No. 28,879/69 isalso driven. The fibre tow is thus drawn onto the take up spool and anyslack in the tow of fibre passing over the rollers 14 and 15 and therollers in the oven is taken up. The release of fibre from the supplyspool 20 is controlled 'by the torque coupling 22 to prevent slippage ofthe fibre on the rollers and the skewing of the rollers 14, 15 advancesthe tow of fibre with succeeding loops separated. The oven is nowbrought'up to temperature.

Using fibres of Courtelle (registered trademark), a polyacrylonitrilefibre containing minor proportions of other constituents, in the formof. a tow comprising a bundle of 10,000 fibres of 1% denier the torquecoupling was set to apply a tension within the range of 8 ozs. to 1 lb.The temperature in the oxidising oven was maintained at 220 C.

It will be seen that with this arrangement in which the fibre tow isprevented from slipping on the internal and external rollers and therollers are driven at the same speed and are of the same diameter, thelength of fibre tow which extends between the external roller 15 and thefirst internal roller 12 at any time ,is kept constant and neithershrinkage nor stretch occurs during this period.

If limited shrinkage or stretch of the length of fibre extending betweenthe roller 15 and the roller 12 is required this can be achieved bymaking the drums 14 and 15 of different diameter and/ or by driving themat a different speed to those inside the oxidising oven for example, bymeans of a gearbox 24. The rates of drive of the rollers 14, 15 and theroller 12 may be such that the fiber therebetween is tensioned withinthe range of percent shrinkage to 20 percent stretch.

I It is to .be noted that the term polyacrylonitrile fibres is used bythose skilled in this art to include co-polymers or terpolymers ofacrylonitrile with other monomers e.g. methyl methacrylate or vinylacetate, either alone or to which have been added polymers compatiblewith them for example phenolic resins or Friedl-Crafts condensates. Itis in this sense that the term polyacrylonitrile fibres isusedthroughout the specification.

We claim:

1. Apparatus for feeding fibres of organic polymer material to anoxidising oven in a process for the manufacture of carbon fibres fromsaid material comprising:

supporting means for carrying a supply of fibres,

tensioning means associated with said supporting means,

a pair of rollers adjacent said oven for supporting successive separatedturns of fibres'from said supporting means in continuous form,

means supporting said rollers for rotation with their axes of rotationin parallel planes,

drive means for driving at least one of said rollers to advance saidsupported fibres towards said oxidising oven, and, driven means withinsaid oven for drawing said fibres into saidoven at a predetermined rate,said drive means driving said roller at a rate such that the fibres areheld taut in passing from said rollers to said driven means within theoven and can only undergo at .most a controlled and limited change inlength compared with its original untreated length and said tensioningmeans being operative'to apply a braking force to said "supporting meanswhereby the length of fibres extending from said supporting means tosaid rollers is maintaified under tension sufiicient to prevent slippageof said fibres on said rollers;

2. Apparatus as claimed in claim l'for the production of'carbon'fibrefrom polyacrylonitrile fibre in which the ra 9? dr e i d ql e s an s i rn means a e such that the fibres extending therebetween are tensioned toa length within the range of from 10 percent shrinkage to 20 percentstretch with respect to their free length.

3. Apparatus as claimed in claim 1 wherein the axes of rotation of saidrollers are skewed with respect to each other in the parallel planeswhereby successive turns of fibres are advanced along said rollers andtheir separation maintained. 7

' 4. Apparatus as claimed in claim 3 wherein the rate of drive of saidrollers and said driven means are such that the fibres extendingtherebetween are held to a length within the range of from 10 percentshrinkage to 20 percent stretch with respect to their free length.

5. Apparatus as claimed in claim 1 for the production of carbon fibresfrom polyacrylonitrile fibres in which said drive means are common tosaid rollers and to said driven means, which latter comprises a drivenroller withm sard OXldlSlHg oven, and all said rollers are of the same 3diameter and the driven rollers are driven at the same speed.

6. Apparatus as claimed in claim 5 wherein the axes of rotation of saidrollers are skewed with respect to each other 1n the parallel planeswhereby successive turns of T fibres are advanced along said rollers andtheir separation maintained.

7. Apparatus as claimed in claim 1 and comprising a gear box fortransmitting drive to said at least one roller to drive said roller suchthat its peripheral speed is 5 different from the predetermined rate ofdrawing said fibres into said oxidising oven.

8. Apparatus as claimed in claim 1 in which said drive means are commonto said rollers and to said driven means, which latter 'comprises adriven roller within said oxldlsmg oven, and said roller within the'ovenis of a carbon fibres of high strength and Youngs modulus wherein acontinuous organic polymer fibre is drawn through an oxidising ovenmaintained at a temperature of about 2Q0 -2 C. and subsequentlycarbonized in a non-carbonrzmg atmosphere, and wherein the fibre travelsbet-ween take-up means comprising supportingmeans and driving meanswithin the oven, the improvement which comprises the step of passing thefibre several times around a pair of rollers disposed adjacent said ovenwiththeir axis in a single plane and skewed to advance said fibre suchthat succeeding turns thereof are maintained out of contact with oneanother, at least one of said rollers being driven to feed said fibre tothe supporting means and driving means in said oven at a rate such thatthe length of fibre extending between the rollers and the take-up .meansin the oven is maintained under a controlled tension.

10. A- process according to claim 9 wherein said tension is such thatsaid length fibre is tensioned to a length within the range 10 percentshrinkage to 20 percent stretch.

References Cited UNITED STATES PATENTS 2,673,385 3/1954 Williamson eta1. 28-59.5 2,692,875 .1o/19s4 Weinstock et al 28-71.3 2,807,863 10/1957Schenker 2859.5X

WILLLAM I. PRICE, Primary Examiner US. 01. X.R. 8-140; 28 72; 68-2, 5;24245

